The present invention relates to a method and to a correspondingly arranged device for storing message or data packets which are present in a particular data transmission format and are to be transmitted or, respectively, routed from a transmitter to a desired receiver in a communication network.
To transmit or route messages, the messages are split into a number of units or data packets in modern telecommunication networks. Each of these data packets is usually provided with a header and a payload field which contains the actual message or payload. In addition, a trailer can be provided as termination of the respective data packet.
As a rule, the information required for routing a data packet is contained in the header of the respective data packet. An Ethernet data packet transmitted, for example, in a MAC (Medium Access Control) frame (which, for the sake of simplicity, will be called eMAC data packet in the text which follows), exhibits, e.g., in the header the source address and the destination address of the message to be transmitted. The destination address of the data packet is analysed at each node of the corresponding communication network in order to determine in dependence thereon the best possible routing path to the desired receiver.
An eMAC data packet also comprises an IP (Internet Protocol) packet and such an IP packet can comprise up to 60 000 bytes. In the switching node of a communication network, the problem may occur that an incoming data packet present in a particular data packet format must be mapped to one or more data packets of another data packet format at the output end. While Ethernet routing is preferably applied in local area networks, ATM (Asynchronous Transfer Mode) routing is used, for example, in more modern broadband ISDN (Integrated Services Digital Network) communication networks. In ATM routing, the messages to be transmitted are transmitted in the form of constant-length data packets, so-called ATM cells and the ATM cells are routed by means of identifiers in the headers. A peculiarity of ATM routing is the fact that each ATM cell always comprises 53 bytes and is composed of a header with 5 bytes and a payload field with 48 bytes. In a switching node of a communication network which exhibits both an eMAC or IP interface and an ATM interface, the problem is, therefore, to map the data of an incoming IP packet which can comprise up to 60 000 bytes to the relatively short ATM cells at the output end, which can in each case only comprise 48 bytes of payload.
In switching nodes or switching facilities such as, e.g. routers or switches, it is therefore necessary to temporarily store the data of an incoming data packet in a buffer. Since it is predominantly the routing information contained in the headers of the individual data packets which is of significance for the routing of data packets in communication networks, the header, as a rule, is processed via a fast data path while the much more extensive payload of the information field of an incoming data packet may have to be subjected to extremely extensive data processing involving the aforementioned temporary storage in order to enable mapping to the desired data transmission format at the output end to be performed.